The beta and contrast values must be scaled to be interpreted as percent signal change, and the beta values themselves are relative to an implicit mean of the signal. The following document may be helpful: http://cibsr.stanford.edu/documents/FMRIPercentSignalChange.pdf
Or, you can report results in a.u. (arbitrary units).
Best regards,
Paul
----- Original Message -----
From: "xiuqin jia" <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, April 5, 2012 10:44:41 PM
Subject: [SPM] Fwd: how to understand beta value
Dear all,
I post my questions again. Hope someone can help me.
thanks,
---------- Forwarded message ----------
From: xiuqin jia <[log in to unmask]>
Date: 2012/4/3
Subject: how to understand beta value
To: [log in to unmask]
Dear experts,
Here, I have two question about Beta value. I have searched it in the SPM
archive, but it seems I cannot understand it completely. So I post it here.
1) Is there a plausible range of beta value?
In my experiment, there are 4 conditions: SI, CI, SA, CA. I extracted the
beta values of the 4 conditions in bilateral DLPFC (dorsolateral prefrontal
cortex) and PPC (posterior parietal cortext). However, It seems a bit
larger than ones in the published papers. I have attached the figure.
I'm not sure, whether is it plausible?
2) Does the negative beta value indicate deactivation?
The positive beta value can be understood as more active, can the negative
beta value be understood as negative activation? How to explain the
negative beta value?
Any comments are deeply appreciated. Thanks a million!
Best Regards,
xiuqin jia
-----------------------------------------------
Xiuqin Jia, Ph.D Candidate
Department of Radiology,
Xuanwu Hospital,
Capital Medial University,
45 Changchun Street,
Xuanwu District,
Beijing, 100053 China
Tel: (+086)-138-1012-5607
--
Xiuqin Jia, Ph.D Candidate
Department of Radiology,
Xuanwu Hospital,
Capital Medial University,
45 Changchun Street,
Xuanwu District,
Beijing, 100053 China
Tel: (+086)-138-1012-5607
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